The objective of this proposal is to develop a novel 3-D ultrasound and elastography system for in vivo imaging of the prostate. Typical transrectal ultrasound systems (TRUS) use a bi-plane probe to obtain two perpendicular B-scans, a sagittal view and longitudinal view. The probe is then manipulated to interrogate the entire prostate region. The results of such a scan can depend heavily on skill of the user since he/she must mentally integrate several images to gain an understanding of the three-dimensional anatomy. In addition, the success of ultrasound-guided biopsies can largely depend on the skill of the operator since the needle must be perfectly aligned within a single scan plane. However, a system capable of in vivo imaging of the prostate in three dimensions could help alleviate some of these problems and therefore show improved clinical value over today's commercial systems. Using an innovative row-column interconnect scheme, 256 x 256 5-10 MHz cylindrical 2-D arrays will be designed, prototyped and tested. This new system will allow for the synthesis of a fully sampled 2-D array capable of dynamic focusing in azimuth and elevation. Since our system will acquire a 3-D volume, new coronal views of the prostate will also be available. To demonstrate proof of concept, a prototype transducer will be integrated with a 64 channel ultrasound research system used to gather the necessary echo information needed to produce cylindrical 3- D volumes. A series of water tank and tissue phantom experiments will be performed to evaluate imaging performance in terms of resolution, contrast, and signal-to-noise ratio. Lastly, a small number of in vitro experiments of canine prostates will be done.